Thomas Dörflein became internationally famous as the guardian of Knut, the polar bear born at Berlin Zoo in 2006 which was rejected by its mother and became the centre of a media frenzy later dubbed “Knutmania”. Knut was credited with a 27 per cent increase in visitors at the zoo in 2007 and profits of almost 7 million euros.

Knut was the first polar bear cub to live past infancy at the zoo in more than three decades. In his first months Dörflein looked after him 24 hours a day, feeding, bathing and playing with him, and sleeping on a mattress next to him at night. He also appeared with Knut in one-hour shows for the public twice a day, play-wrestling with him and standing by as he pottered about before adoring fans. Such was Dörflein’s dedication that he was awarded Berlin’s Medal of Merit.

Thomas Dörflein was born in 1963 in Berlin. He did a three-year apprenticeship at Berlin Zoo and at first was responsible for apes, big cats and mountain goats. He was put in charge of the bears in 1987.

It was on December 5, 2006, that Tosca, a grouchy ex-circus bear, gave birth to Knut and a twin. When she put them out on a rock in the enclosure to die the keepers scooped them out in a net, took them inside and started feeding them milk and cod-liver oil. Only Knut survived, emerging from an incubator after 44 days. “The first time he looked at me with those blue eyes, that was it,” Dörflein later said.

Knut’s surroundings were not, of course, quite authentically polar. He had a teddy bear and a football, and was given his own Christmas tree. Dörflein even played him Elvis Presley songs on his guitar, discovering, in the process, that You’re the Devil in Disguise sent him to sleep. The whole situation unsettled a number of zoologists and animal rights activists, who in March 2007 declared that it was unacceptable for a bear to be so dependent on human beings. One animal rights campaigner, Frank Albrecht, said that hand-feeding was “a grave violation of the animal protection laws” and that allowing Knut to continue as he was was “condemning the bear to a dysfunctional life”. The comments provoked a public outcry and brought about a new debate about the right to life.

But the zoo stated that Knut would not be put down or left to fend for himself, and he appeared in public for the first time soon afterwards. He caused a sensation, inspiring such headlines as “Polar baby melts hearts” and “I’m Knuts about you”; he became a mascot for Berlin, and Knut merchandise of all kinds appeared, followed by a children’s book and a film.

The “Knut show” at the zoo attracted thousands of visitors. Dörflein found that he had suddenly become a celebrity. He received hundreds of letters from women, some of them proposing marriage; it was his evident paternal instinct that attracted them, he thought. He never quite got used to the camera flashes in front of the enclosure, and turned down invitations to appear on talk shows.

As Knut grew, Dörflein took him on daily walks around the zoo to build up his muscles, and slowly started to distance himself to reduce separation trauma later on. Dörflein stopped appearing with Knut in shows in July last year when the zoo’s director decided that Knut had grown too big for him to play with keepers safely. Knut now weighs more than 265lb.

Dörflein is survived by his partner, Daniela, her young son, and by two grown-up children from a previous relationship.

Thomas Dörflein, zoo keeper, was born in 1963. He died of a heart attack on September 22, 2008, aged 44